1. Field of the Invention
This invention relates to a method of an emboss pattern process, emboss pattern processing apparatus, and an embossed sheet, which is used for the production of an optical precision embossed sheet, such as a reflector, a prism sheet, a fresnel lens and so on.
2. Description of the Related Art
In recent years, a reflective ability sheet (a plastic reflection sheet), undergoing a micro-prism process on the surface of a thermoplastic resin sheet, has been employed in the reflection panel field, the fashion field, an architecture field and so on.
In the United States, the use of a glass bead type and a cube corner type are approved as the aforementioned reflective ability sheet. Commonly, the reflective ability sheet of the glass bead type is superior in short-distance visibility, and the reflective ability sheet of the cube corner type is superior for long-distance visibility and luminance created by optical reflection.
In the production of the reflective ability sheet of the cube corner type, an emboss pattern on an emboss pattern forming die (or a pattern embossing die) should be precisely transferred onto the thermoplastic resin sheet.
Therefore, it is especially important that the thermoplastic resin sheet is pressed onto the emboss pattern forming die (or the pattern embossing die) with appropriate pressure, and further, the pressure is continuously added for a predetermined period of time.
As conventional methods for producing the reflective ability sheet serving the above requirement, for example, a continuously pressing method (Japanese Patent Application Publication No. Sho60-56103), a belt method (Japanese Patent Application Publication No. Hei5-17023), and a roller method (an example relating to FIG. 9 in Japanese Patent Application Publication No. Hei3-43051) are proposed.
With the continuously pressing method, emboss pattern forming dies (or pattern embossing dies) are sequentially pressed onto a sheet material of solid phase, laid on a belt and continuously supplied with plural pressing means having a heating or cooling function to transfer patterns onto the sheet material.
With the belt method, a belt having an emboss pattern and a thermoplastic resin sheet are pressed between a pair of rollers to transfer patterns onto the sheet.
With the roller method, an emboss pattern is transferred onto a sheet by using a roller forming the emboss pattern on its outer circumferential face.
According to the aforementioned continuously pressing method, the production speed is slow and apparatus is complicated and large in size.
According to the belt method, the belt itself carries the emboss pattern, so that apparatus is large in size, and a disadvantage arises concerning the endurance of the belt as a pattern embossing die.
And, according to the roller method, the production speed is faster and the endurance is better. But, the temperature of the sheet is not effectively controlled to increase when the emboss pattern is transferred onto the sheet and decreased when the sheet after being embossed is peeled from the roller, resulting in disadvantages concerning the pattern reproducibility and the peeling properties. In other words, the apparatus is not structured to have a large difference in temperature between an area of the roller where the pattern is transferred, and an area of the roller where the sheet is peeled, thus not allowing the precise pattern reproducibility and the smoothly peeling properties to be obtained.
And further, the reflective ability sheets obtained by the conventional producing methods are not satisfied in regard to the reflecting properties.
A method of an emboss pattern process according to the present invention is characterized by including the following steps of: transferring an emboss pattern onto a thermoplastic resin sheet by using an emboss patterning roller; lustering (setting a gloss on) the opposite face of the embossed face of the thermoplastic resin sheet by using a lustering means having a mirror face member; and peeling the thermoplastic resin sheet from the emboss patterning roller at a lower temperature than a temperature for transferring the emboss pattern.
It is advisable that the temperature for transferring the emboss pattern is defined to be more than the Vicat softening point of the thermoplastic resin sheet, though also depending upon the type of resin used, the temperature of the thermoplastic resin sheet before being embossed, and so on. The Vicat softening point is a softening temperature of the thermoplastic resin sheet, in which the measuring method of the above temperature is based on JIS K7206.
A difference in the temperature in the pattern transfer step and the lower temperature than that in the pattern transfer step can be properly defined, for example, more than 10xc2x0 C., preferably more than 20xc2x0 C., also depending on the pressure or the type of resin. The difference in temperature of less than 10xc2x0 C. causes the lack of cooling ability in the peeling step, so that the precise embossed pattern cannot be obtained. The upper limit of the difference in temperature is not especially defined, but it is preferable to be less than 150xc2x0 C. In the difference in temperature of more than 150xc2x0 C., the endurance of the roller becomes inferior or the production speed becomes slower, resulting in higher cost.
When the thermoplastic resin sheet is lustered by the lustering means, the face-pressure is more than 0.01 MPa. If the face-pressure decreases less than 0.01 MPa, the uniformity of gloss is likely to deteriorate.
Incidentally, a thermoplastic resin film having a relatively different thickness from the then no plastic resin sheet can be used.
Emboss pattern processing apparatus according to this present invention is characterized by including: an emboss patterning roller for transferring the emboss pattern onto a thermoplastic resin sheet; a lustering means, having a mirror face member, for lustering the opposite face of the embossed face of the thermoplastic resin sheet; and a cooling means for cooling the thermoplastic resin sheet peeled from the emboss patterning roller, to a lower temperature than a temperature for transferring the emboss pattern.
In the emboss pattern processing apparatus according to the present invention, it is advisable that the emboss patterning roller has a roller body having a face for embossing a pattern; and a sealing ring attached on each side face of the roller body, in which the roller body and the sealing ring are formed with a passage for flowing a temperature controlling medium for cooling from the one sealing ring through the roller body to the other sealing ring.
As the temperature controlling medium, water, silicone oil, oil for controlling temperature, or the like can be selectively used.
According to the present invention, the passage is formed along an area of the roller body which is required to be cooled, and the temperature controlling medium with the suitable temperature is flown into the passage, thereby the temperature when the thermoplastic resin sheet is peeled off the emboss patterning roller is decreased to be lower than the temperature when the pattern is embossed. In other words, the aforementioned passage for flowing the temperature controlling medium comprises a cooling means.
The temperature controlling medium with the fixed temperature is continuously flowed from one sealing ring through the roller body to the other sealing ring, thereby allowing the temperature of the area of the roller body which is required to be cooled to be accurately controlled.
The passage in the roller body can be plural passage-tubes formed along and in the vicinity of the outer circumferential face of the roller body.
The diameter of the passage-tube and the number of passage-tubes are selectively decided so that the temperature of the area of the roller body which is required to be cooled is effectively controlled by the temperature controlling medium flown through the aforementioned passage-tubes. And, the suitable diameter of the passage-tube and the suitable number of passage-tubes may be determined according to the size of the roller used.
Where the passage-tube is a sectional circle, the inner diameter is selectively decided, preferably, for example, approximately 1 mm to 100 mm. Depending upon the temperature of the temperature controlling medium, but if the inner diameter is less than 1 mm, the sufficient flow rate cannot be obtained. But, if the inner diameter is more than 100 mm, the amount of temperature controlling medium for cooling remaining in the passage-tube increases, so that the heating efficiency in rotating the roller from the area for peeling the sheet toward the area for transferring pattern decreases. It is advisable that the sealing ring is formed therein with a groove linking to the plural passage-tubes of the all passage-tubes in the roller body.
For example, when the area of the roller body where the temperature is needed to be controlled is defined at a xcex8 degree angle originating from the axis of the roller body, the groove can be formed to flow the temperature controlling medium into the passage-tubes in the area created by the xcex8 degree angle. The xcex8 degree angle is decided according to the pattern transfer speed, and is not especially limited. But where the xcex8 degree angle is defined at an extremely small value, it is impossible to effectively control the temperature. Where the xcex8 degree angle is defined at an extremely large value, it is difficult to control the temperature in the cooling step or the heating step when the passage for flowing the temperature controlling medium for heating is further formed in order to simultaneously carry out the cooling step and the heating step.
It is desirable that the sealing ring is formed therein with a passage for flowing a temperature controlling medium for heating in addition to the passage for flowing the temperature controlling medium for cooling; and the sealing ring is formed therein with grooves linking to the passages.
The cooling medium and the heating medium flow into the two passages, so that the heating medium flows through the area of the roller where the pattern is transferred, and the cooling medium flows through the area of the roller where the sheet is peeled, thus creating the large difference in the temperature for improving the pattern reproducibility and the peeling properties
It is desirable that the degree of surface roughness of the mirror face member of the lustering means is less than 3S.
If the degree of surface roughness if more than 3S, the luminance decreases because light irregularly reflects on a non-embossed face of the thermoplastic resin sheet. Preferably, it is less than 1S.
The mirror face member can be a metal belt having the mirror face, a metal-faced elastic roller having the mirror face, or the like.
The belt is preferably made of stainless. The thickness of the belt is defined selectively, for example, 0.3 mm to 1.5 mm, preferably, 0.5 mm to 0.8 mm.
The metal-faced elastic roller has a tubular metal member located on the outer surface of the metal-faced elastic roller and a tubular elastic member located inside of the tubular metal member.
The roller body has an outer cylinder section having the face for embossing the pattern; a middle cylinder section inserted into the inside of the outer cylinder section and having the passage; and an inner cylinder section inserted into the inside of the middle cylinder section, in which the middle cylinder section has a greater linear expansion coefficient than that of the outer cylinder section, and the inner circumferential face of the middle cylinder section is formed to be a tapered shape having the same degree angle as a tapered shape of the outer circumferential face of the inner cylinder section.
The middle cylinder section is heated while being inserted into the outer cylinder section, thereby the middle and outer cylinder sections are coupled to each other because of the difference of the thermal expansion coefficients of both sections.
Further, the inner cylinder section is inserted into the middle cylinder section during the aforementioned heated expansion after the middle cylinder section is inserted into the outer cylinder section, and then the inner and middle cylinder sections are united by a shrinkage force created when the temperature of the sections returns from the high temperature to a room temperature.
In the emboss pattern processing apparatus according to the present invention, it is advisable that the roller body of the emboss patterning roller is coupled with a rotation shaft for rotating the roller body, rotation shaft to pass through the sealing rings.
More specifically, in the emboss pattern process, only the roller body is rotated and the aforementioned sealing ring is in a stationary position. Therefore, the temperature controlling medium flows into only the passage-tubes in the roller body which are linked to the groove in the stationary sealing ring by rotating the roller body.
Preferably, a heating means for heating an area of the roller before the emboss pattern is transferred is provided in the vicinity of the emboss patterning roller.
The specific example of the heating means is selectively decided, for example, an infrared heater and so on. The area of the roller where the pattern is transferred is effectively heated by the outside heating means.
The emboss pattern can be a cube corner type.
The embossed sheet according to the present invention is produced by the following method: transferring an emboss pattern onto a thermoplastic resin sheet by using an emboss patterning roller; lustering the opposite face of the embossed face of the thermoplastic resin sheet by using a lustering means having a mirror face member; and peeling the thermoplastic resin sheet from the emboss patterning roller at a lower temperature than a temperature for transferring the emboss pattern.
The conditions, as to the temperature when the emboss pattern is transferred, the temperature when the thermoplastic resin sheet is peeled from the emboss pattern roller, and so on, are the same as the conditions explained in the method for the emboss pattern process according to the present invention.
The specific type of the used thermoplastic resin is selectively decided. But where the embossed sheet is used as a plastic reflecting plate, the ideal material is an amorphous resin, such as polyvinyl chloride, polycarbonate, acryl resin (PMMA or the like), and so on, because of the high transparency and that the pattern embossed on the sheet is not easily transfigured even in the shrinkage.
And further, the thickness of the thermoplastic resin sheet is not particularly defined, but, preferably it is, for example, approximately 0.07 mm to 30 mm. If it is thinner than 0.07 mm, the pattern-transferring properties can deteriorate, and if it is thicker than 30 mm, the heating and cooling efficiency or the efficiency of production can deteriorate.